U.S. patent number 7,335,231 [Application Number 10/755,701] was granted by the patent office on 2008-02-26 for containment system for constraining a prosthetic component.
This patent grant is currently assigned to Smith & Nephew, Inc.. Invention is credited to Terry McLean.
United States Patent |
7,335,231 |
McLean |
February 26, 2008 |
Containment system for constraining a prosthetic component
Abstract
Methods, systems and devices for preventing prosthetic
articulating surfaces from separating from each other. A
containment system according to one embodiment seeks to prevent an
implant stem head from dislocating from a prosthetic component
while providing an increased range of motion over conventional
contrained components. In one embodiment, an implant structural
member includes a cavity and an opening having a lip, including a
web along a portion of the lip. An implant stem head has a
cooperating surface that corresponds with the web, so that when the
cooperating surface of the implant stem head is aligned with the
web, the head may be inserted into the implant structural member.
The implant stem head is then rotated and the femoral stem
component attached, thereby preventing dislocation of the head.
Inventors: |
McLean; Terry (Cordova,
TN) |
Assignee: |
Smith & Nephew, Inc.
(Memphis, TN)
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Family
ID: |
23004832 |
Appl.
No.: |
10/755,701 |
Filed: |
January 12, 2004 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20040143341 A1 |
Jul 22, 2004 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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10057284 |
Jan 24, 2002 |
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60264153 |
Jan 25, 2001 |
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Current U.S.
Class: |
623/22.15;
623/22.21; 623/22.4; 623/22.18 |
Current CPC
Class: |
A61F
2/32 (20130101); A61F 2/3609 (20130101); A61F
2002/30827 (20130101); A61F 2002/3493 (20130101); A61F
2002/30495 (20130101); A61F 2002/365 (20130101); A61F
2002/3208 (20130101); A61F 2310/00017 (20130101); A61F
2002/3625 (20130101); A61F 2002/30448 (20130101); A61F
2/34 (20130101); A61F 2250/0026 (20130101); A61F
2002/30652 (20130101); A61F 2002/345 (20130101); A61F
2/3676 (20130101); A61F 2002/30354 (20130101); A61F
2002/30405 (20130101); A61F 2220/0033 (20130101); A61F
2/36 (20130101); A61F 2002/30332 (20130101); A61F
2002/3611 (20130101); A61F 2002/30187 (20130101); A61F
2002/3216 (20130101); A61F 2230/0034 (20130101); A61F
2310/00179 (20130101); A61F 2/4241 (20130101); A61F
2/40 (20130101); A61F 2310/00023 (20130101); A61F
2002/3448 (20130101); A61F 2220/005 (20130101); A61F
2002/30685 (20130101); A61F 2002/3233 (20130101); A61F
2220/0025 (20130101); A61F 2/4637 (20130101); A61F
2002/30477 (20130101); A61F 2002/30322 (20130101); A61F
2002/30449 (20130101) |
Current International
Class: |
A61F
2/42 (20060101); A61F 2/32 (20060101) |
Field of
Search: |
;623/20.12,20.13,20.24,21.17,22.15,22.18,22.19,22.28,22.38,22.43,23.35,22.21,22.4 |
References Cited
[Referenced By]
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WO |
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Primary Examiner: Snow; Bruce
Attorney, Agent or Firm: Kilpatrick Stockton LLP
Parent Case Text
RELATED APPLICATIONS
This is a continuation of application Ser. No. 10/057,284, filed
Jan. 24, 2002, now abandoned, which claims priority to Provisional
Application No. 60/264,153, filed Jan. 25, 2001 entitled, "Captive
Head for Bipolar Endoprosthesis," each of which is incorporated by
reference herein.
Claims
The invention claimed is:
1. A containment system comprising: (a) a shell, the shell
comprising a cavity and an outside surface and including at least
one opening on the outside surface providing access to the cavity;
(b) a liner, the liner comprising: an outer surface; a lip; and an
inner surface, the inner surface forming a cavity and including a
web, wherein the web extends around a portion of the lip to form a
D-shaped opening; (c) an implant stem head, the implant stem head
comprising: a generally spherical body having a surface configured
to correspond to the web enabling the implant stem head to be
inserted into the liner when the implant stem head is in a first
orientation; and a cavity; and (d) a separate femoral stem
component which may be inserted into the cavity of the implant stem
head, wherein the shell may be received by an acetabulum, and
wherein the liner may be received in the cavity of the shell, and
wherein the web allows the implant stem head to be inserted into
the cavity of the liner when the implant stem head is oriented in
the first orientation and constrains the implant stem head within
the cavity of the liner when the implant stem head is oriented in a
second orientation such that the implant stem head may articulate
within the liner but cannot be removed from the liner once it is
attached to the stem.
2. A containment system comprising: (a) a shell, the shell having a
generally hemispherical shape and comprising a cavity and an
outside surface and including at least one opening on the outside
surface providing access to the cavity, wherein the shell is
received by an acetabulum; (b) a liner, the liner having a
generally hemispherical shape and comprising: an outer surface; a
lip; and an inner surface, the inner surface forming a cavity and
including a web, wherein the web extends around a portion of the
lip to form a substantially D-shaped opening, and wherein the liner
is received in the cavity of the shell and may articulate within
the cavity of the shell; (c) an implant stem head, the implant stem
head comprising: a generally spherical body having a substantially
planar surface configured to correspond to the web enabling the
implant stem head to be inserted into the liner when the implant
stem head is in a first orientation; and a cavity; and (d) a
separate femoral stem component which may be inserted into the
cavity of the implant stem head, wherein the inner surface of the
liner is shaped to correspond generally to the outer surface of the
implant stem head, and wherein the web is shaped to cooperate with
the implant stem head as the implant stem head articulates relative
to the liner, and wherein the web allows the implant stem head to
be inserted into the cavity of the liner when the implant stem head
is oriented in the first orientation and constrains the implant
stem head within the cavity of the liner when the implant stem head
is oriented in a second orientation such that the implant stem head
may articulate within the liner but cannot be removed from the
liner.
3. A containment system comprising: (a) an implant structural
member, the implant structural member comprising: an outer surface;
a lip; and an inner surface, the inner surface forming a cavity and
including a web, wherein the web extends around a portion of the
lip to form a substantially D-shaped opening; (b) an implant stem
head, the implant stem head comprising: a generally spherical body
having a substantially planar surface configured to correspond to
the web enabling the implant stem head to be inserted into the
implant structural member when the implant stem head is in the
first orientation; and a cavity; and (c) a separate femoral stem
component which may be inserted into the cavity of the implant stem
head, wherein the outer surface of the implant structural member
may be received by a shell, and wherein the implant stem head may
be received by the implant structural member, and wherein the web
allows the implant stem head to be inserted into the cavity of the
implant structural member when the implant stem head is oriented in
a first orientation and constrains the implant stem head within the
cavity when the implant stem head is oriented in a second
orientation.
Description
FIELD OF THE INVENTION
The invention is directed generally to methods, systems and devices
related to prosthetic implants, including a device for preventing
prosthetic articulating surfaces from separating from each other,
and more specifically to a device for preventing an implant stem
head from dislocating from an a prosthetic component.
BACKGROUND OF THE INVENTION
Artificial implants, including hip joints, shoulder joints and knee
joints, are widely used in orthopedic surgery. Hip joint prostheses
are common. The human hip joint acts mechanically as a ball and
socket joint, wherein the ball-shaped head of the femur is
positioned within the socket-shaped acetabulum of the pelvis.
Various degenerative diseases and injuries may require replacement
of all or a portion of a hip using synthetic materials. Prosthetic
components are generally made from either metals, ceramics, or
plastics.
Total hip arthroplasty and hemi-arthroplasty are two procedures
well known within the medical industry for replacing all or part of
a patient's hip. A total hip arthroplasty replaces both the femoral
component and the acetabular surface of the joint, so that both a
femoral prosthesis and an acetabular prosthesis are required. A
conventional acetabular prosthesis may include a cup, a cup and a
liner, or in some cases only a liner, all of which may be formed in
various shapes and sizes. Generally, a metal cup and a polymeric
liner are used. However, the liner may be made of a variety of
materials, including polyethylene, ultra high molecular weight
polyethylene and ceramic materials. The cup is usually of generally
hemispherical shape and features an outer, convex surface and an
inner, concave surface that is adapted to receive a cup liner. The
liner fits inside the cup and has a convex and concave surface. The
cup liner is the bearing element in the acetabular component
assembly. The convex surface of the liner corresponds to the inner
concave surface of the cup or acetabulum, and the liner concave
surface receives the head of a femoral component. An acetabular cup
may include a highly polished inner surface in order to decrease
wear.
The liner concave surface, or internal concave surface, is
characterized by features relative to an axis through the center of
the concave surface. This axis may or may not be aligned with the
central axis of the shell. In a typical liner the concave surface
has a hemispherical geometry and is also referred to as the
internal diameter. In such liners, the geometry is characterized by
features that are concentric to an axis that runs through the
center of the internal diameter.
An acetabular prosthesis may be fixed in the reamed acetabulum of a
patient. Such a prosthesis may include a cup (or a cup and liner
assembly) that is fixed either by placing screws through apertures
in the cup or by securing the cup with cement. In some cases, only
a liner is cemented in a patient due to poor bone stock. In other
cases, a cup having a porous surface may be press fit into the
reamed acetabular surface.
A femoral prosthesis used in total hip arthroplasty generally
includes a spherical or near-spherical head attached to an elongate
stem with a neck connecting the head and stem. In use, the elongate
stem is located in the intramedullary canal of the femur and the
spherical or near-spherical head articulates relative to the
acetabular component. Femoral prostheses used in total hip
arthroplasty procedures may or may not differ from an
endoprosthesis used in a hemi-arthroplasty, described below.
However, the femoral head of each type prosthesis is generally a
standard size and shape. Various cups, liners, shells, stems and
other components may be provided in each type arthroplasty to form
modular prostheses to restore function of the hip joint.
Hemi-arthroplasty refers to replacing part of a hip joint, such as
replacing a femoral component so that a femoral prosthesis
articulates against natural body tissue in the patient's
acetabulum. A femoral prosthesis implanted during a
hemi-arthroplasty is generally referred to as an endoprosthesis.
Generally, an endoprosthesis includes a stem, a head, and may
include additional components such as shells and liners. Current
endoprosthesis designs include (1) monoblock; (2) two-component;
(3) three-component; and (4) five-component designs. A monoblock
endoprosthesis is a one-piece structure including a femoral stem
and head. Polarity refers to the number of articulating surfaces a
prosthesis contains. A monoblock endoprosthesis has one
articulation surface between the head and the patient's natural
acetabulum, and is therefore referred to as monopolar.
A two-component endoprosthesis includes a femoral component and a
shell. The femoral component may include a modular head and stem. A
two-component design may be bipolar, so that the head articulates
relative to the shell and the shell articulates relative to the
acetabulum. A three-component endoprosthesis includes a femoral
component, a liner, and a shell. Similar to a two-component design,
the femoral component may include a modular head and stem. A
three-component endoprosthesis may either be: bipolar, in which the
liner is fixed in the shell; or tripolar, in which the head
articulates relative to the liner, the liner articulates relative
to the shell, and the shell articulates relative to the acetabulum.
A five-component endoprosthesis includes a femoral component (which
may include a modular head and stem), a first liner, a first shell,
a second liner, and a second shell. Both of the first and second
liners are fixed inside each of the first and second shells.
Therefore, this design is a tripolar design: the second shell is
free to articulate with respect to the acetabulum, the modular head
of the femoral component articulates with respect to the first
liner and the first shell articulates relative to the second liner.
Thus, endoprostheses may be described both with respect to the
number of components and with respect to the number of articulating
surfaces as installed in a patient. Some current designs may also
include a mechanical device, such as a snap-ring, for constraining
the femoral head, further described below.
Endoprostheses, as well as total hip prostheses, may also be
described as constrained and non-constrained prostheses.
Non-constrained prostheses rely on the downward force of the body
through the joint and the tension created by the soft tissue,
including the muscles, ligaments and tendons, to retain the
prosthesis in its implanted position. Other prostheses include
mechanisms for preventing dislocation of the components, such as
the implant stem head. Typically, these prostheses have restraint
mechanisms that result in a smaller range of motion of the hip
joint, and are generally referred to as "constrained"
components.
One example of a restraint mechanism is a shell or liner having
greater than hemispherical coverage around the head such that the
head is constrained within the internal diameter, thus preventing
subluxation and dislocation. In contrast to standard liners,
constrained liners employ an extended, elevated portion over a
segment of the periphery of the liner internal diameter in order to
increase coverage of the femoral head and thus reduce the
likelihood of dislocation and aid in reduction of the head should
subluxation occur. While use of a constrained components is
generally not desirable due to resulting decreased range of motion,
the use of constrained components may be beneficial in cases of
tenuous stability in order to avoid dislocation. See e.g. T. Cobb,
et al., The Elevated-Rim Acetabular Liner in Total Hip
Arthroplasty: Relationship to Postoperative Dislocation, Journal of
Bone and Joint Surgery, Vol. 78-A, No. 1, January 1996, pp. 80-86.
However, constrained components have a reduction in the arc of
motion to contact in the direction of the elevated lip segment,
thus, there is a substantial loss of overall range of motion
compared to a standard liner. An implant stem head constrained by a
shell or liner may dislocate if the femoral component rotates
beyond the range of motion permitted by the assembly. Dislocation
may occur because the edge or lip of the liner or shell that
retains the implant stem head acts as a fulcrum about which the
femoral component pivots, thereby causing the implant stem head to
dislocate from its position within the liner or shell of the
prosthesis. Dislocation of a hip prosthesis is painful and often
requires medical intervention.
Three component bipolar endoprostheses including polyethylene
liners are known in the industry, and suffer from at least three
major clinical problems. First, the vast majority of articulation
occurs between the liner and the shell, and it is not uncommon to
obtain almost no relative motion between the shell and the
acetabulum. Second, there is often a considerable amount of
polyethylene wear debris generated from the device due to fatigue
loading of the liner. Finally, there is a lower limit to the size
of the shell due to the need to incorporate a standard head size
and an appropriately thick liner. Current solutions to these
problems include a design having a ceramic shell, a ceramic head
and a polyethylene snap ring, which locks the head in the shell.
Such designs frequently lead to polyethylene wear and have a
complex assembly. Another solution has been use of a unipolar
monoblock device, which does not require a liner but which results
in excessive wear of the acetabulum.
Thus, there exists a need for a prosthetic component capable of
retaining an implant stem head to prevent it from dislocating while
providing a larger range of motion than is allowed by conventional
constrained prostheses. There is also a need for a prosthetic
component capable of retaining an implant head to prevent it from
dislocating while eliminating the requirement of an inner bearing
surface, or liner.
SUMMARY OF THE INVENTION
Set forth below is a brief summary of systems and methods according
to the invention that addresses the foregoing problems and provides
benefits and advantages in accordance with the purposes of the
present invention as embodied and broadly described herein. A
prosthesis according to one embodiment of this invention provides a
constrained prosthesis with an increased range of motion over
current constrained prostheses. According to one embodiment of this
invention, a constrained prosthesis prevents dislocation of a
femoral component. A prosthesis of this invention may be used with
humans and animals and may be used with conventional hip prostheses
including endoprostheses and prosthesis used in total hip
arthroplasty.
A containment system according to one embodiment of this invention
includes an implant structural member having a generally spherical
outer surface and having a cavity and opening adapted to receive an
implant stem head or other prosthetic component. The opening of the
cavity of the implant structural member includes a lip having a web
for retaining the implant stem head within the cavity and
preventing it from dislocating. The web comprises only a portion of
the lip forming the opening. As a result, the femoral component is
able to travel through a larger range of motion than the range of
motion provided a femoral component coupled to a conventional
constrained prosthesis. In one embodiment, a portion of an outer
surface of the implant stem head is configured to correspond to the
web on the shell. An implant stem head according to one embodiment
of this invention includes an aperture adapted to receive a femoral
stem component.
A containment system according to one embodiment of this invention
is assembled by first aligning the surface of the implant stem head
configured to correspond to the web of the implant structural
member in a first orientation so that it corresponds to the web.
The implant stem head is then inserted into the implant structural
member and rotated until the head aperture is visible through the
opening in the implant structural member. The implant stem head
cannot be oriented in the first orientation where the surface of
the head corresponds with the web while the femoral stem component
is coupled to the implant stem head. Therefore, the implant stem
head cannot be removed from the implant structural member unless
the femoral stem is first removed. As a result, the femoral
component cannot dislocate while positioned within a patient.
One feature of a containment system according to one embodiment of
this invention is the elimination of the risk of dislocation of a
femoral component.
Another feature of a containment system according to one embodiment
of this invention is a constrained prosthetic component providing
an increased range of motion.
Yet another feature of a containment system according to one
embodiment of this invention is that a containment system is
inexpensive to manufacture and includes few parts.
Another feature of a containment system according to one embodiment
of this invention is the elimination of the need for a polyethylene
liner, allowing the use of a larger head diameter with a resulting
increase in range of motion and elimination of the possibility of
polyethylene wear.
Yet another feature of a containment system according to one
embodiment of this invention is a containment system that is easy
to assemble and that requires no additional instruments for
assembly.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and form a
part of the specification, illustrate preferred embodiments of the
present invention and, together with the description, disclose the
principles of the invention.
FIG. 1 is a perspective view in cross-section of a containment
system according to one embodiment of this invention incorporated
within a two-component endoprosthesis.
FIG. 2 is an exploded perspective view of the system of FIG. 1.
FIG. 3 is an exploded perspective view of an implant structural
member and implant stem head of one embodiment of a containment
system according to this invention.
FIG. 4 is an exploded perspective view of the shell and implant
stem head of FIG. 3, rotated 180 degrees.
FIG. 5 is a top plan view of the implant structural member of FIG.
1.
FIG. 6 is a top plan view of an implant structural member according
to an alternative embodiment of this invention.
FIG. 7 is a side elevation view in cross-section of the implant
structural member and implant stem head of FIG. 3.
FIG. 8 is a side elevation view in cross-section of the implant
structural member and implant stem head of FIG. 7, as
assembled.
FIG. 9 is a side elevation view in cross-section of the implant
stem head and shell of FIG. 8 after the head has been rotated to
receive a stem.
FIG. 10 is a side elevation view in cross-section of the implant
stem head, shell and stem of FIG. 1, as assembled.
FIG. 11 is a side elevation view in cross-section of the implant
stem head, shell and stem of FIG. 1, as assembled and rotated.
FIG. 12 is a perspective view in cross-section of a containment
system according to one embodiment of this invention incorporated
within a three-component endoprosthesis.
FIG. 13 is a perspective view in cross-section of a containment
system according to one embodiment of this invention incorporated
within a five-component endoprosthesis.
FIG. 14 is an exploded perspective view of a containment system
according to an alternative embodiment of this invention.
FIG. 15 is a side elevation view in cross-section of the shell and
implant stem head of FIG. 14.
FIG. 16 is a side elevation view in cross-section of the shell and
implant stem head of FIG. 14, as assembled.
FIG. 17 is a side elevation view in cross-section of the shell and
implant stem head of FIG. 14, as assembled and rotated.
DETAILED DESCRIPTION OF THE DRAWINGS
Methods, systems and devices according to this invention seek to
provide a containment system for preventing prosthetic articulating
surfaces from separating from each other while allowing an
increased range of motion over conventional constrained prosthesis.
One embodiment of a containment system according to this invention
seeks to provide a hip prosthetic component for constraining an
implant stem head of a femoral component while providing an
increased range of motion. Generally, a containment system
according to one embodiment of this invention, includes an implant
structural member having a cavity and an opening to receive an
implant stem head. The opening includes a lip and a web along a
portion of the lip. The containment system also includes an implant
stem head having a cooperating surface with a shape that
corresponds with the shape of the web. The implant stem head is
adapted so that it may only be inserted into and removed from the
implant structural member when the cooperating surface of the head
is aligned with the web.
A containment system according to one embodiment of this invention
is assembly by aligning the cooperating surface of the implant stem
head with the web of the implant structural member and inserting
the implant stem head into the implant structural member. The
implant stem head is then rotated and the femoral stem component is
attached. The implant stem head can only be removed from the
implant structural member if the stem is first removed from the
head, allowing the cooperating surface of the implant stem head to
be oriented with the web. In this manner, the head is constrained
in the implant structural member as long as the stem and head are
assembled.
Consider one example of systems and devices according to this
invention. Containment system 10 is illustrated as a two-component
bipolar endoprosthesis in FIGS. 1 and 2. This containment system 10
includes an implant structural member 14, such as a shell, adapted
to receive implant stem head 12, which is adapted to be coupled to
femoral stem component 13, the implant stem head and femoral stem
component forming a femoral component when assembled. As shown in
FIGS. 1 and 2, implant structural member 14 is adapted to fit
within acetabulum 11 and is adapted to capture and retain implant
stem head 12. Implant structural member 14 includes a cavity 16
that has a generally spherical shape and that is formed by an inner
surface 18 and an opening 20. Opening 20 includes lip 36 having web
22, which reduces the size of opening 20 so that opening 20 forms a
D-shape, as shown in FIG. 5. In an alternative embodiment, shown in
FIG. 6, web 22 includes curved edge 31, which allows the femoral
stem component to rotate through a slightly larger range of motion.
In other embodiments, web 22 has other suitable shapes.
Implant stem head 12 may or may not extend beyond opening 20 of
implant structural member 14. For example, as shown in FIGS. 1-2
and 10-11, implant stem head 12 extends beyond opening 20 of
implant structural member 14, but head 12 and member 14 may also be
adapted so that head 12 does not extend beyond the opening 20. For
example, as shown in FIGS. 3-4 and 7-9, implant structural member
14 is adapted to receive implant stem head 12 such that head 12
does not extend beyond opening 20 of implant structural member 14,
but may also be adapted so that head 12 does extend beyond the
opening 20. In one embodiment, the plane of web 22 is at a right
angle to the lip 36; however, in an alternative embodiment, the
plane of web 22 is at any suitable angle relative to the lip. The
description of the two component containment system 10 is generally
applicable to all embodiments shown in FIGS. 1-11, with the only
difference being the positioning of the implant stem head relative
to the implant structural member, as described above.
As shown in FIG. 7, first tangent line 30 and second tangent line
32 are not parallel. Instead, first tangent line 30 is at an angle
.alpha. that is less than 90 degrees relative to reference line 34,
which is parallel to second tangent line 32. Web 22 is formed as a
continuation of inner surface 18 and maintains the same radius of
curvature as other portions of inner surface 18. Thus, web 22 is
formed by extending inner surface 18 beyond reference line 34 to
form angle .alpha., as shown in FIG. 7. In this configuration, web
22 decreases the diameter across opening 20 and does not create a
surface likely to cause unnecessary wear on implant stem head
12.
Implant stem head 12 is generally spherical in shape and includes a
cooperating surface 24 that enables implant stem head 12 to be
inserted within cavity 16 of implant structural member 14. Surface
24 may be flat, as shown in FIGS. 1-4, or may be formed of
alternative shapes that correspond to the shape of the web. As
shown in FIG. 7, cooperating surface 24 is positioned on implant
stem head 12 so that a diameter 15 of implant stem head 12 taken
perpendicular to cooperating surface 24 and traveling through the
center of implant stem head 12 is slightly smaller than distance 17
within opening 20. This configuration allows implant stem head 12
to be inserted into cavity 16 by aligning cooperating surface 24
with web 22. Orienting cooperating surface 24 in this manner allows
implant stem head 12 to be inserted into cavity 16 past web 22, as
shown in FIG. 8.
After implant stem head 12 has been completely inserted into cavity
16 of implant structural member 14, head 12 is rotated so that head
12 is retained in cavity 16. Specifically, after implant stem head
12 is rotated, head 12 cannot be removed from implant structural
member 14 because the diameter 19 of implant stem head 12, shown in
FIG. 7, is greater than distance 17 of opening 20, and cooperating
surface 24 is no longer oriented to correspond with web 22, as
shown in FIG. 9. A femoral stem component 13 is then coupled to
head 12, preventing alignment of cooperating surface 24 with web 22
so that head 12 is retained in implant structural member 14. Once
femoral stem component 13 has been coupled with head 12, head 12
cannot be removed from shell 14 until femoral stem component 13 has
been removed because stem 13 prevents head 12 from being rotated so
that cooperating surface 24 aligns with web 22.
As shown in FIGS. 7-9, implant stem head 12 includes cavity 26,
which is adapted to receive femoral stem component 13 and which is
generally cylindrical. In an alternative embodiment, cavity 26 may
be conical, cubical, or any other suitable shape. In other
alternative embodiments, cavity 26 may include threads, barbs,
rings or any other suitable mechanical connectors to couple head 12
to stem 13. In yet another embodiment, adhesive or cement may be
used to couple head 12 to femoral stem component 13.
In one embodiment, opening 28 of cavity 26 of implant stem head 12
is positioned on cooperating surface 24. In this embodiment,
opening 28 is positioned to receive stem 13 only after implant stem
head 12 has been rotated to expose opening 28, as shown in FIG. 9.
Attachment of stem 13 to implant stem head 12 prevents implant stem
head 12 from being rotated so that implant stem head 12 can be
removed from cavity 16, as shown in FIG. 10. Specifically, after
implant stem head 12 has been attached to stem 13, stem 13 contacts
the lip 36 of opening 20 and prohibits implant stem head 12 from
being rotated any further, as shown in FIG. 11. Thus, lip 36 of
opening 20 defines the range of motion of femoral stem component
13. In another embodiment, opening 28 is positioned within head 12
at a location other than within surface 24. For instance, opening
28 may be located adjacent to surface 24 or in another location on
head 12. During use, web 22 is preferably positioned superiorly, as
shown in FIG. 2, in order to maximize range of motion and minimize
the possibility of subluxation.
In one embodiment according to this invention, off-axis
eccentricity is provided. In one embodiment, negative eccentricity
is provided, forcing rotation of the implant structural member
relative to the acetabulum. In another embodiment, positive
eccentricity is provided, resulting in an increased range of motion
of the femoral component. For example, as shown in FIGS. 7-9, the
center of rotation 37 of implant stem head 12 is not positioned in
the same location as the center of shell 39. Center of rotation 37
of implant stem head 12 is positioned closer to opening 20 than the
center of shell 39. As a result, the femoral component is less
restricted than if both center of rotation 37 and the center of
shell 39 were located in the same position.
In one embodiment of this invention, implant stem head 12 is
ceramic and implant structural member 14 is a ceramic shell. This
embodiment does not include polyethylene in any form, reducing wear
debris. In one embodiment, implant stem head 12 is larger than a
conventional head, allowing an increased range of motion resulting
from the increased diameter of the assembly. In one embodiment, the
throat diameter of the shell is reduced to slightly less than a
complete hemisphere, further increasing range of motion.
An alternative embodiment of a containment system according to this
invention is illustrated as a three-component tripolar
endoprosthesis in FIG. 12. Containment system 41 is very similar to
the two-component embodiment described above, with the retention
mechanism located within liner 38. For example, containment system
41 includes a shell 46 having a cavity 40 for receiving liner 38.
Shell 46 is adapted to be received in acetabulum 43. Liner 38 is
adapted to be received in cavity 40 of shell 46 and includes a
cavity 47 adapted to receive implant stem head 48. Cavity 47 of
liner 38 is defined by an inner surface 42 and opening 44. Inner
surface 42 can be formed from any conventional process. As
described in the two-component endoprosthesis embodiment above, a
web 50 on the lip of liner 38 is positioned to capture an implant
stem head 48 and to prevent dislocation of implant stem head 48
while the stem 45 is coupled to head 48.
Yet another alternative embodiment of a containment system
according to this invention is illustrated as a five-component
endoprosthesis in FIG. 13. Similar to the embodiment of FIG. 12,
the retention mechanism of containment system 72 is located on
first liner 74, which is adapted to receive implant stem head 76.
First shell 78 is adapted to receive first liner 74, while second
liner 80 is adapted to receive first shell 78. Second liner 80 is
received in second shell 82, which is received in acetabulum 84.
First liner 74 includes a web 86 and captures and retains head 76
as described in the embodiments above.
In an alternative embodiment, shown in FIGS. 14-17, a containment
system includes shell 54 having two webs 56, 57, each positioned on
opposing sides of opening 58 of shell 54. Implant stem head 60
includes two cooperating surfaces 62, 63 that correspond with webs
56, 57 so that implant stem head 60 may be inserted into cavity 64
of shell 54. In this embodiment, the containment system functions
in the same manner as the embodiments having a single web. For
example, implant stem head 60 is positioned so that surfaces 62, 63
correspond with webs 56, 57 as shown in FIGS. 14 and 15. Implant
stem head 60 is then inserted into shell 54, as shown in FIG. 16.
Implant stem head 60 is then rotated until cavity 66 of head 60 is
capable of receiving a femoral stem component 70 through opening
68, as shown in FIG. 17. Other alternative embodiments of a
containment system according to this invention may include shells
or liners having any appropriate number of webs that may be
configured as shown or in alternative configurations, such as
three, four or five webs and having heads corresponding to the
webs.
The components of the various prostheses described may be made from
metal, such as stainless steel and titanium, ceramic, plastic, such
as polyethylene, or any other suitable material. In one embodiment,
all of the components of a two-component bipolar endoprosthesis are
metal. In an alternative embodiment, all of the components of a
two-component bipolar endoprosthesis are ceramic. In another
embodiment, the shell and implant stem head of a three-component
endoprosthesis are either metal or ceramic, while the liner is
polyethylene.
The embodiments of a containment system as described above all
relate to endoprostheses used in hemi-arthroplasty. Similar
embodiments of a containment system according to this invention may
be incorporated into a prosthesis used in total hip arthroplasty,
using a web to constrain a femoral head component. Alternative
embodiments of a containment system according to this invention may
be utilized to capture and retain other prosthetic components. For
example, a web may be incorporated into a second liner of a five
component endoprosthesis in order to capture and retain the first
shell and first liner assembly. Additionally, embodiments of a
containment system according to this invention may also be used to
capture components of other orthopedic prosthesis, such as shoulder
prosthesis and small finger joint prosthesis. For example, a
constrained shoulder prosthesis may include a web to capture and
retain the humeral head.
One method of using one form of structure according to this
invention is as follows. Implant stem head 12, shown in FIG. 7, is
positioned to be inserted into shell 14 by orienting implant stem
head 12 in a first orientation so that cooperating surface 24
corresponds with web 22. As shown in FIG. 8, implant stem head 12
is inserted into shell 14 so that the outside surface of implant
stem head 12 contacts inside surface 18 of shell 14. Implant stem
head 12 is then placed in a second orientation by rotating head 12
so that cavity 26 is exposed and in position to receive femoral
stem component 13. After femoral stem component 13 has been coupled
to implant stem head 12, head 12 cannot be removed from shell 14
unless stem 13 is first removed because stem 13 prevents head 12
from being oriented in a first orientation where cooperating
surface 24 corresponds with web 22. The endoprosthesis is then
surgically implanted, so that the stem of the femoral component is
implanted into the femur of a patient. The endoprosthesis is then
implanted in the acetabulum of a pelvis.
The foregoing is provided for purposes of illustrating, explaining,
and describing embodiments of this invention. Modifications and
adaptations to these embodiments will be apparent to those skilled
in the art and may be made without departing from the scope or
spirit of this invention or the following claims.
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